Currently, the majority of autonomous and mobile electronic systems are powered by electrochemical batteries. Although battery quality has substantially improved over the last two decades, their energy density has not greatly increased. At the present time, issues such as cost, weight, limited service time and waste disposal (all intrinsic to batteries) are impeding the advance of many areas of electronics. The problem is especially acute in the area of portable electronic devices, where rapidly growing performance and sophistication of mobile electronic devices leads to ever-increasing power demands that electrochemical batteries are unable to meet.
One of the technologies that holds great promise to substantially alleviate current reliance on the electrochemical batteries is high-power energy harvesting. The concept of energy harvesting works toward developing self-powered devices that do not require replaceable power supplies. In cases where high mobility and high output power are required, harvesters that convert mechanical energy into electrical energy are particularly promising, inasmuch as they can tap into a variety of high power density energy sources, including human locomotion.
High power harvesting of mechanical energy is a long-recognized concept that has not been commercialized in the past due to the lack of a viable energy harvesting technology. Traditional methods of mechanical-to-electrical energy conversion such as electromagnetic, piezoelectric or electrostatic do not allow for effective “direct coupling” to the majority of high-power environmental mechanical energy sources. Bulky and/or expensive mechanical or hydraulic transducers are often required to convert a broad range of aperiodic forces and displacements typically encountered in nature into a force accessible for conversion using those methods.
Recently, a new approach to energy harvesting has been demonstrated. In particular, a high-power, microfluidics-based energy harvester has been developed, as disclosed in U.S. Pat. Nos. 7,898,096 and 8,053,914 issued to the present inventors and incorporated herein in their entirety. The energy harvester as disclosed in this prior work generates electrical energy through the interaction of thousands of microscopic fluid droplets with a network of thin-film electrodes, where this combination has been found to be able to generate several watts of power. In one preferred embodiment, a train of energy-producing droplets is disposed in a thin channel and is hydraulically actuated by a force differential applied to the opposing ends of the channel. This type of energy generation provides an important advantage as it allows efficient direct coupling with a wide range of high-power environmental mechanical energy sources, including human locomotion.
A method for energy harvesting using microfluidic devices that improves upon the above-described arrangement is based on a synergistic combination of these techniques with the classical magnetic method of electrical power generation (based on Faraday's law of electromagnetic induction), as described in our co-pending application Ser. No. 13/352,588 filed Jan. 18, 2012 and incorporated by reference herein. The resulting approach has a number of substantial advantages over the prior arrangements, including its ability to provide for greatly increased power output, providing effective energy generation without requiring the use of external bias voltage sources. The ability to eliminate the need for external bias voltage sources improves the harvester performance characteristics, enhances its reliability and simplifies the harvester design when compared to the other prior art arrangements.
While the above-described energy generation methods have proven the ability to generate useable amounts of electrical energy (on the order of watts) from harvesting mechanical energy (such as human locomotion), some shortcomings still remain. In particular, no provision is made in any of these arrangements for allowing a continuous, revolving motion of the chain of energy-producing elements within a closed-loop, energy-producing channel.